Although the dielectric constant of plasma depends on electron collision time as well as wavelength and plasma density, experimental studies on the electron collision time and its effects on lasermatter interactions are lacking. Here, we report an anomalous regime of lasermatter interactions generated by wavelength dependence (1.2–2.3 µm) of the electron collision time in plasma for laser filamentation in solids. Our experiments using timeresolved interferometry reveal that electron collision times are small (<1 femtosecond) and decrease as the driver wavelength increases, which creates a previouslyunobserved regime of light defocusing in plasma: longer wavelengths have less plasma defocusing. This anomalous plasma defocusing is counterbalanced by light diffraction which is greater at longer wavelengths, resulting in almost constant plasma densities with wavelength. Our wavelengthscaled study suggests that both the plasma density and electron collision time should be systematically investigated for a better understanding of strong field lasermatter interactions in solids.
Wavelength scaling of electron collision times in filamentproduced plasma in solids
We report an anomalous regime of lasermatter interactions, which is created by the wavelength dependence of electron collision time during filamentation in solids. Experiments are performed using femtosecondtimeresolved interferometry by varying the filament driver wavelength from 1.2 to 2.3 μm and using a 0.8μm probe. Information on the phase and absorption via interferometry enables simultaneous measurements of plasma densities and electron collision times during filamentation. Although it is expected that the plasma density decreases with increasing wavelength due to larger plasmadefocusing at longer wavelengths [14], our measured plasma densities are nearly constant for all the pump wavelengths. This observation is successfully explained by the measured wavelengthdependence of electron collision time: electron collision times in filamentproduced plasma decrease with increasing wavelength, which creates an anomalous regime of plasmadefocusing where longer wavelengths experience smaller plasma defocusing. In addition, simulations with the measured electron collision times successfully reproduce the observed plasma density scaling with wavelength [5].
[1] L. Bergé et al., Phys. Rev. A 88, 023816 (2013). [2] Y. E. Geints et al., Appl. Opt. 56, 1397 (2017). [3] S. Tochitsky et al., Nat. Photonics 13, 41 (2019). [4] R. I. Grynko et al., Phys. Rev. A 98, 023844 (2018). [5] Nagar et more »
 Award ID(s):
 2010365
 Publication Date:
 NSFPAR ID:
 10271700
 Journal Name:
 Bulletin of the American Physical Society
 ISSN:
 00030503
 Sponsoring Org:
 National Science Foundation
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Abstract 
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